Scientists Claim A Piece of Earth Survived Apocalyptic Melt

As previously reported on Outer Places, researchers recently discovered that the birth of the moon most likely occurred when a planet dubbed Theia collided with Earth. According to this model, the collision would have released a great deal of debris that then congealed to form the moon, and the Earth would have undergone an apocalyptic melting. At the end of this process, the entire Earth would have been a giant ball of magma. The Earth's mantle would have then cooled beneath the crust, retaining the same isotopic signatures throughout.

However, Sujoy Mukhopadhyay et al from Harvard University recently found that the the ratio of helium-3 to neon-22 is much lower in the deeper part than in the shallow part. The team explains this heterogeneity by postulating that the melt was not global; rather, the side that collided with Theia melted and released gases, while the rocky side that was far away from the impact site retained its gases, causing the initial imbalance. Then, the rocky side spread out and formed its own layer of rock in the mantle, which caused the imbalances within the mantle that Mukhopadhyay and his team observed.

"We think that the observations we have made provide some of the cleanest evidence that the Earth didn't completely melt," says Mukhopadhyay.

There was also an imbalance within the Earth's mantle of the amounts of xenon-129. Since xenon-129 comes from the radioactive decay of iodine-129, its prevalence can be used as a time stamp in order to study the Earth at various stages. The xenon signature suggests that the formation of this layer of rock occurred approximately 4.45 billion years ago, which could provide insight into the Earth's early stages. "That is really exciting, because we can now probe these different stages," says Mukhopadhyay.

We also may be able to learn more about the elusive Theia as a result of these differing compositions. Since the moon was formed from Theia, the differences we observe between the moon and this portion of the Earth could give us insight into Theia's chemical properties.